Process for tanning hides and skins



Patented 4, 1 930 UNITED STATES PATENT OFFICE- IDIUND GREG STIASN Y, OI DABMSTADT, GERMANY, AND BENZION J'ALOWZEB, OI

PARIS, FRANCE I v PROCESS FOR TANNING HIDE S AND SKINS Io Drawing. Application fled January 8, 1927, Serial ll'o. 158,814, and in Germany November 30, 1988.

The invention relates to the tanning of hides and skins with'the use or joint use of complex iron compounds, these latter being understood to mean in a very general way 5 those compounds in which the iron is present in a more or less extremely disguised form and in which h drolysis is apparently dimin ished. It has een found that tanning with iron can be carried .out with particularly good results, while avoiding the disadvantage characteristic of the iron tanning processes hitherto proposed, by treating the hides and skins to be tanned with compounds of iron .and sulphites or with substances capable of forming the same.

The complex compounds of sulphites and iron to be employed according to the invention as tanning agents, can be produced for instance by the action of metallic sulphites,

for example alkali sulphites, or of bisulphites and metabisulphites or of mixtures of sulphite and bisulphite or of mixtures of alkaline-reacting substances with sulphites, bisulphites or both upon ferric salts, for instance ferric chloride, ferric sulphate, ferric formate, ferric acetate, ferric lactate and the like, if desired basic ferric salts, or upon ferrous salts in the presence of or with the subsequent action of oxidizing agents or by the action of sulphurous acid upon iron compounds rea'cting therewith. Other substances, more especially also substances hav ing atannin action or additions usual in the tanning industry, electrolytes or nonelectrolytes may be present at the same time.

It has been found advisable when employing sulphites, for instance Na SO to use as iron salt, ordinary ferric salts or moderately basic ferric salts, whereas whcn'employing bisulphites, such as for instance NaHSO these are preferably caused to react with strongly basic ferric salts. It has been found that strongly basic ferric salts cannot support any appreciable quantities of Na SO 'without being precipitated and that ferric salts that are not'basic or only slightly basic do not as a general rule producestable and satisfactory tanning liquors with NaHSO When working with mixtures of sulphites and bisulphites, for instance of Na,SO, and

NaHSO, use may be made of ferric salts of varying basicity. The necessary degree of basicity of the'ferric salt can be reached in ways already known, for instance by the addition of sodium carbonate, sodium hydroxide, sodium silicate, ammonia, borax and other substances capable of converting ferric salts into basic salts.

The formation of the complex ferri-sulphite compounds is usually apparent from a considerable deepening in colour as soon as the reaction components are mixed together. Moreover the presence of the former complex compounds may be recognized by the relatively slight hydrolysis which is indicated for instance by the slight acidity of the aqueous solutions, as well as by the complete or partial prevention or retarding of the usual reactions of iron, for instance with potassium ferrocyanide, potassium thiocyanate and the like.

In carrying the invention into effect the method adopted may for'instance be such that the com ounds of iron and sulphites are produced y combining their components in an aqueous, preferably concentrated solution and these original solutions containing the formed complex compounds are then used as an addition to the tanning liquors. Instead of employing this method it is also possible for instance to introduce the components forming the complex compounds directly into the tanning liquor and allow the complex compounds to form in the latter or in the hide substance. In some cases it'has been found advantageous to cause the components. forming the complex compounds to act successively upon the hides or skins to be tanned, for instance in such a way that the pelts are first of all treated with a solution containing only one component, for instance with a ferric chloride or ferric sulphate solution and the secondcomponent, for example alkali sulphite or bisulphite is added subsequently. The successive treatment can also take place in separate baths. In some cases the method adopted may also ,be such that the hide is first treated with compounds-composed of sul bites and ferrous salts and the latter are then converted into compounds complex ferri-sulphite compounds composed of sulphites and ferric salts by treatment with suitable oxidizing agents.

For the purpose of producing the iron sulphite compounds use may be made in place of or in addition to metallic sulphites or bisulphites, or organic derivatives of sulphurous acid, together with carbohydrates or substances of like nature or products prepared from carbohydrates or the like, such as for example starch-syrup, molasses and the like. It is possible in this way to obtain complex compounds which are characterized by particularly good effects. For producing complex compounds of this kind or tanning liquors containing them the method adopted may for instance be such that aferric salt, a metallic sulphite or bisulphite, for instance an alkali sulphite and the organic components, for instance molasses are combined in suitable roportions. By this means it is possible or instance to obtain a ferri-sulphite-glucose-liquor which is extremely stable with respect to the action of alkali and even with soda lye can be made strongly alkaline to phenolphthalein and can be boiled in a strongly alkaline solution without preci itating. A behaviour of this kind is not s own either by sulphite-free iron-glucose-liquors or glucose-free ferri-sulphite liquors. The use of complex ferri-sulphite compounds containing organic components, such as carbohydrates and the like has proved particularly advantageousfor certain-combined tanning processes. They may be employed with marked success for instance in combination with vegetable tanning agents, in which case synthetic tanninglagents, which may be used if desired to aci 'fy the li nor, may also be added with advantage to-t e liquor.

Compounds of sulphurous acid with other organic'substances such as for example aldel hydes, ketones and the like may also be used for producing the ferri-sulphite compounds. Complex compounds of organic acids or salts of organic acids especially aliphatic acids such as formic, acetic, butyric, malonic,-citric and the like with sulphurous acid or its salts,

for instance ulphites, may also be employed instead of t e metallic sulphites or'bisulphltes herein efore referred to for producing (Cf. B. 11 91351531111 and Aellig, Helv. chim. acta 6, 37,

The tanning operation can be carried out byemploying the methods usual for metallic tanmng, more especially for iron tanning. The tanning with iron according to the invention may be combined with other tanning methods, for instance in such a manner that other tanning agents or admixtures usual in the tanning industry may be added or a preliminary or after-treatment with such substances may be provided in addition to the iron tanning. Combined efiects of most varied nature can be obtained by the comjected to a preliminary pickling or swelling treatment or not.

In carrying out the present tanning process it has been found that the proportions of for example the ferric salt on the one hand and for instance'the sulphite on the other hand are of importance for obtaining the desired results. It is possible for instance by choosing the proportions of the components to affect for instance the basicity,-the extent to which the action of the iron is rendered less apparent and the electrophoretic direction of migration of the complex'iron compound, as well as the intensity of the tanning action. while taking intov consideration the other conditions, for instance the composition of the tanning liquors, the duration of the tanning and the like, to adjust the proportions of ferric salt and sulphite or the like if necessary by means of preliminary experiments. In general, goods results are obtained when use is made of for instance 1 5 mol. sulphite to 1 mol. ferric salt. The quantity of sulphite to be added varies essentially also according to the basicity of the ferric salt employed.

The use of complex iron-sulphite compounds has the advantage that .the hide is uniformly and thoroughly tanned, that a particularly good grain is obtained and that the tanned leather can be e'asilystuifed, dyed and curried. The shrinkage temperature of leather tanned with ferro-sulphite liquors is considerably higher than that of leather tanned in the usual waywith basic ferric chloride or ferric sulphate liquors. A, further advantage of the leather obtained a0- 1 cording to the invention is itscapacity of being unafi'ected bystoring.

I Examples 1. 100 k pickled pelts are placed in a liquor whic has been prepared in the cold by the interaction of a solution of 10 kg. ferric chloride and a solution of 55 kg; ,sodium'sulphite. (Volume of the liquor about 200-400 L.) During tanning, further quantities of concentrated stock solution are added if necessary. When'the tanning is complete the leather is treated'further in the usual way.

2. 100 kg. non-pickled peltsare subjected to a preliminary tanning in a 33% basic fer ric sulphate liquor, prepared from a solution of 12 kg. ferric sulphate in 30 L. water and It is therefore advisable,

a solution of 3.2 kg. calcined soda and kg." common salt in 20 L. water (volume of the liquor about 200-400 L.). After the preliminary tanning a solution of 25 kg.

crystallized sodium sulphite in 70 L. water is poured into the preliminary tanning liquor and the treatment continued until the pelts have been tanned thorough-1y to the desired extent.

3. 100 kg. pelts are placed in a tanning liquor which is prepared as follows 7.5 kg. ferric chloride are dissolved in 20 L. water, this solution is neutralized with 3 kg. calcined soda and then mixed with kg. sodium lactate dissolved in L. water. The liquor is diluted to about 200-300 L. and the pelts kept in movement in it until they are thoroughly penetrated by the tanning liquor. If it is desired to continue the tanning to a further extent and make the leather more resistant to higher temperatures, it is placed in a second bath, consisting of kg. NagSO3 in 150200 L. water and moved about in this for 35 hours. lVhen the tanning is complete, the leather is allowed to lie for a few-days,

then Washed and treated further in the usual up to 150 L. liquor. 100 kg. pelts are tanned in this solution. If further tanning is desired, a solution of kg. sodium sulphite in 150 L. water is added to the liquor during tanning.

5. A solution composed of 17 kg. sodium sulphite and 2.5 sodium bisulphite in 1 L.

water, which has approximately the pH-value of water, is added to 30 kg. of a sulphite cellulose extract. This mixture is added to a solution of 3.7 kg. ferric chloride in 10 L. water and the whole is made up to 200 L. liquor. 100 kg. pickled ox hides are tanned in this liquor. If necessary an additional treatment with a liquor of the same composition is carried out.

We claim:

1. A tanning agent comprising substances capable of forming complex ferric-sulphite compounds.

2. The process of tanning hides and skins, which comprises treating the material to be tanned with a bath comprising a complex ferric-sulphite compound. I

3. The process of tanning hides and skins, which comprises treating the material to be tanned with a bath comprising substances capable of forming complex ferric-sulphite compounds. 1

4. The process of tanning hides and skins, which comprises treating the material to be tanned with a bath comprising complex ferric-sulphite compounds and other substances employed in the tanning industry.

5. The process of tanning hides and skins which comprises treating the material to be tanned with a bath comprising substances capable of forming complex ferric-sulphite compounds and other substances employed in the tanning industry.

6. The process of tanning hides andskins, which comprises treating the material to be tanned with a bath comprising complex ferric-sulphite compounds and organic components of the nature of carbohydrates, having the property of increasing the stability of the aforesaid compounds.

7. The process of tanning hides and skins,

which comprises treating the material to be tanned with a bath comprising substances capable of forming complex ferric-sulphite salts during the tanning process.

8. The process of tanning hides and skins, which comprises treating the material to be tanned with a bath comprising a series of substances which form complex ferric-sulphite salts during the tanning process.

9. The process of tanning hides and skins, which comprises treating the material to be tanned with a bath comprising different baths comprising a series of substances which form complex ferric-sulphite salts during the tanning process.

10. A tanning agent comprising a complex ferric-sulphite compound containing at least one aliphatic carboxylic acid radicle.

11. A tanning agent comprising a complex ferric-sulphite compound containing several aliphatic carboxylic acid radicles.

12. The process of tanning hides and skins,

'Which comprises treating the material to be tanned with a bath comprising substances capable of forming complex ferric-sulphite compounds containing at least one aliphatic carboxylic acidradicle.

13. The process of tanning hides and skins, which comprises treating the material to be tanned with a bath comprising substances capable of forming complex ferric-sulphite compounds, containing several aliphatic carboxylic acid radicles.

14. A tanning agent comprising complex ferric-sulphite compounds.

3 In testimony whereof we aflix our signatures.

EDMUND GEORG STIASNY. BENZION JALOWZER. 

